1. Field of the Invention
The present invention relates to a composite electronic part, and particularly to composite electronic part such as a laminated LC filter and the like having a dielectric ceramic portion and a magnetic ceramic portion which are co-sintered.
2. Description of the Prior Art
In a conventional laminated LC filter which is the background of the present invention, a dielectric ceramic portion and a magnetic ceramic portion are bonded together directly by pressing and bonding a dielectric green sheet and a magnetic green sheet before firing.
However, in the conventional laminated LC filter in which the dielectric ceramic portion and the magnetic ceramic portion are bonded together directly, due to a mutual diffusion produced between the dielectric ceramic portion and the magnetic ceramic portion during firing, insulation resistance drops, or due to a concentrated stress occurred between the dielectric ceramic portion and the magnetic ceramic portion during firing, the bonding interface between the dielectric ceramic portion and the magnetic ceramic portion sometimes separates.
Furthermore, in the conventional laminated LC filter, as is disclosed in Japanese Patent Provisional Publication No. 90915/1984, No. 172804/1983 and Japanese Patent Publication No. 33247/1984, a layer consisting of a mixture of dielectric material, magnetic material, glass and metal is formed between the dielectric green sheet and the magnetic green sheet, which are fired to form an intermediate layer between the dielectric ceramic portion and the magnetic ceramic portion.
In the conventional laminated LC filter in which the intermediate layer is formed between the dielectric ceramic portion and the magnetic ceramic portion, the stress between the dielectric ceramic portion and the magnetic ceramic portion produced by firing is relaxed. In such a conventional composite electronic part in which the intermediate layer is formed, since the dielectric ceramic portion and the magnetic ceramic portion are co-sintered at a low temperature of 1000.degree. C. or less, in the case of using a Pb group dielectric material as the material of the dielectric ceramic portion and a Ni--Zn group ferrite material as the material of the magnetic ceramic portion, the mutual diffusion between the dielectric ceramic portion and the magnetic ceramic portion can not be prevented, and thus it is not effective as the intermediate layer. When glass is mixed into the intermediate layer, a glass component is diffused to deteriorate electrical characteristics in some cases.
As such, the property of the intermediate layer between the dielectric ceramic portion and the magnetic ceramic portion depends greatly on material compositions of the dielectric ceramic portion and the magnetic ceramic portion. And hence, as the material of the intermediate layer, the material which is adaptable to that of the dielectric ceramic portion and the magnetic ceramic portion must be selected. When the material which is not adaptable to that of the dielectric ceramic portion and the magnetic ceramic portion is used as the material of the intermediate layer, the function as the intermediate layer can not be exhibited and it can not be used as the complex electronic part.